I have questioned the placing of a radiator under a window many times, the problem is the thermostat traditionally is on the opposite wall, so in most cases either the radiator is on outside wall which means hotter air against outside wall, or thermostat on outside wall which means it reads lower than actual as cooled by outside wall.
However place thermostats around the room and it becomes apparent air does not move that fast, at moment thermometer on living room window sill is showing 31.7°C but radiator just below the window is showing 20°C and one diagonally to it shows 22°C. Clearly the thermals are not evening out the room temperature.
In mothers house I experimented with thermostat position, and found setting on the low side and close to radiator actually worked better than opposite wall sitting on the gas fire so not in contact with the wall but thermals are slow moving the air around, so you get a large hysteresis if the thermostat is too far from heat source.
So at the side of the heat source low down around an inch from it is not so bad as it seems, and my TRV with duel sensors that compensates for water temperature is to be far rather good at controlling the room temperature.
The chimney effect is well known, so two panels with a gap between them works far better than a larger area but no chimney effect, which is why the double panel radiators works better than old school type cast iron type.
This all means what works A1 in one house can be rubbish in another, which is why the rules of thumb often don't work, like not putting a TRV in same room as a wall thermostat, it will work where the room is normally cool, has no outside doors, and no alternative heating and is on entrance floor, but on the entrance floor every one of my rooms has an outside door, except for toilet/shower room and with an extractor fan and radiator set reasonable high as one gets undressed in that room, that is not suitable either.
So one needs to think, and weigh up how house is likely to heat, and how best to control in your house, not walk around blinkered. Life style also matters, retired it is rare the house in winter does not have one of us in the house, so some room is always being heated. But when younger it was common for house to be empty 7 am to 6 pm, so heating could be off while not at home, the return time was variable and I looked at geofenceing and occupancy detection, however the TRV I have does not have a learning ability (think the Hive one has?) so the anti-hysteresis software means the temperature raise tappers off sharply as the target is approached, so heat from 10°C to 18°C reasonable quickly, but 18°C to 20°C quite slow, and in the main house does not cool to 10°C it only cools to 17°C so the geofenceing and occupancy detection means coming home to a house nearly as cold as it would be if you manually turned on the heat when you came through the door, again time taken from work place to home will change that, but for many people simple timed works better.
Some "Smart" thermostats do work out the time taken to heat the home, Nest wall thermostat and as said the Hive TRV I think does that, so it can heat flat out until the crucial point and then start reducing the output, without over shooting, and for geofencing that is important, however the Hive TRV costs around £50 and a simple programmable TRV costs £10 so it seems we are looking at £40 per unit to get reasonable control required for geofenceing and occupancy detection.
So I googled "electric heater with geofenceing and occupancy detection" and got
this result the price tag of £432 is rather off putting. When I can get a
heater from Argos at £37 how long would it take to save £395?
It seems we have all the controls for wet central heating, but with non centralised heating there are not enough made, so we look at silly prices. So maybe we need a return to the old Economy 7 wiring even if not the tariff, so all heaters can be switched on as we start on our way home? Well not me I am retired, but those who will likely be forced into electric heating.
Look back just 30 years ago, and although we had RCD's to buy a box with a RCD for every circuit would cost an arm and a leg, today they are stocked in every electrical whole sale outlet. So in even 15 years time likely electric heater with geofenceing and occupancy detection will be common place and cheap, do you remember the prices for the early LED watches, my friend in around 1975 paid around £200 for one, a year latter LCD came out and it was worthless.
So at moment I would keep it simple, and wait and see what market forces cause to be made. I was telling everyone how bad Hive was compared with Nest, then Hive released their TRV head and Nest withdrew support for the one that worked with their wall thermostat, so they have switched position. Now wish I had Hive not Nest. But in 6 months time would not be surprised to see a Nest TRV so maybe they will swap again.
So some one in 6 months time will find these posts as say what a load of nonsense because some thing new has been released.
