Polo bike geometry + addons

isolating out the effect of, say 10mm less trail or 1 degree more head angle nigh-on impossible
got to disagree. I've been running an adjustable setup for over a year now. A degree makes a noticeable difference to low speed handling and 10mm of trail is huge!

To make the point, If you do a trackstand your front wheel will naturally want to sit at the point where your wheel will jack-knife. (the more you lean the less your wheel wants to be turned too.) You can visibly see the difference it makes due to the point where your wheel will sit and will feel much heavier through the bars as you turn. In practise, more trail lets you turn much tighter and stops having to pedal so much to correct understeer.

As a little experiment:
If you have a cartridge headset you can run a split-ring instead of the crown race and space it up and down using standard headset spacers. Not a long term setup but will give you a feel for what a difference these small things make.