Can a bed heater be smaller than the bed and still give good results?

I have a TRONXY X5ST-400 that I built from a kit. When I first powered it on, the control board immediately exploded, so I have been working on reworking it to use an SKR 1.3. Unfortunately, it appears the original board took the tack of converting its input power to 12V for all outputs (including heater outputs), but the SKR 1.3 does not do this. The board shipped with a 24V power supply, but all the components are 12V components, and the SKR 1.3 wants to output 24V to them. I have wired up the fans with buck converters and am looking to replace the heater cartridge with a 24V unit. Where I'm stuck right now is figuring out how to configure a bed heater. The printer came with an aluminum sheet with, I believe, a PCB-style bed heater stuck to the bottom. The stock heater is a 12V unit that should be about 165W based on my measurements. A complicating factor is that almost all available heaters are upgrades to this paltry power level, but the PSU on the printer can only deliver 360W total power. I could upgrade the PSU too and use a 24V bed heater, but after some research, it's looking like the most affordable way to move forward will be to purchase a silicone heating pad that runs on wall power, and then use an SSR to control it from the SKR 1.3. But even there, I'm having a hard time ticking all the boxes:

• 400x400
• Runs on 120 VAC
• Uses about 350W, give or take (the stock heater is a 12V unit that should be about 165W based on my measurements -- haven't yet found a parts list for this printer!)
• Affordable

I am asking myself at this point whether it would really be so bad to use a 300x300 heater centred on the bed, and then just not worry too much about the bed heat at the very edges, which shouldn't be entirely off anyway because the aluminum should spread the heat, right? Is this a thing people do? Does it work okay?

Any other insight greatly appreciated. :-)

as long as you have an aluminium bed - then it should be fine. You might need to boost the temps to get the edges, but aluminium conducts heat well.

Not sure how well it would work on an all glass bed though.

Thanks for your reply :-) I'll proceed then with a 300x300 heater on the 400x400 aluminum plate, and I'll give an update once I know how it's going. :-)

A 300x300 silicon pad stuck to the bottom of the 400x400 aluminum print bed (which has an integrated 12/24VDC heating circuit that I'm not using) seems to be working quite well. The heat takes a minute or two to get through the glass, but it gets there and seems relatively even, though I haven't tried to print anything at the edges at this point. :-)