Calculating how big a base to attach to a chair to prevent it toppling

I have a pair of cinema seats that are designed to be bolted to the floor.

I don’t want to do this so instead I have made wooden feet and bolted the seat to them and they are quite stable.

I know that an object won’t topple if its centre of mass lies within its base, so I simply made the feet extend to the rear of the seat back and the front edge of the seat base when folded down. Now they look quite large, so I’d like make the feet as short as possible. The seats do not recline.

I’m pretty sure the centre wooden foot has no effect on front/back stability so can be reduced to be just a few CM longer than the metal plate it is bolted too (for aesthetic reasons).

For the 2 outer feet, can I experiment with the tipping point by standing the chairs (with feet attached) on other wooden blocks with I can move forwards and backwards?

I also have another pair with no feet attached yet, and they will tip backwards if stood up, but with someone sitting in them they will freestand, and are quite difficult to tip backwards but relatively easy to tip forwards, which tells me that they only need to extend perhaps 10-15cm backwards.

Question: How do I calculate how short the feet can be without sacrificing stability?

Assume 2 normal sized adults.