I suspect your car started life with a non adjustable ARB, no 36 with the mounts onto the chassis. Then had what was an adjustable ARB from an S1/S2 Sport pack car fitted, as that was all was available at the time, no 46 - bear in mind it’s both adjustable and stiffer than the standard ARB. Then later cars had 46a fitted as it used the holes in the chassis that the standard non adjustable ARB had.
As ever, you can argue this any which way you want!
The early set up, using the bushes mounted to the lower wishbone mount bolt were fine, until you went even stiffer than the Lotus bar, then the bolt flexed instead of the bar. The bushes tended to wear quite quickly, then rattled over bumps.
The late set up, using the chassis mount were fine, until you went stiffer than the Lotus bar, then the lower chassis mount flexed instead of the bar. The bushes are better, as they are an aluminium bracket, with a thin plastic bearing inside.
Personally I’d rather flex a cheap replaceable bolt, than a not cheap, not replaceable chassis.
As to whether a fatter bar will help your car, that depends on millions of options, spring rate, damper set up, tyres, car weight, geo, etc, etc. Have you played around with the setting of the bar on track to see whether it’s the same, better or worse on soft, middle or hard setting?
Yes, harder is nearer the front of the car.
Is the rolling causing an issue? Faster or slower between stiffer/softer?
Making it too stiff on the bar can be unpleasant - especially on the road - but equally too soft is not ideal.
FWIW, I have foolishly set mine to full hard - and as a consequence of that, I find the car has so little roll that I swear I’m slower around the track - it takes away some of the cues that let you know you’re nearing the limit of grip and it seems to have made the rear come out a little more suddenly too? Not sure if that’s even possible, but it genuinely feels that way. I’m intending to put mine back to ‘middle’ hardness