I've just started a new character and when going through minefield, I noticed that I need to be right on top of the mines (accidentally setting some off) in order to have the cursor connect with them so I can disarm them from a safe distance.

Previously, I had a good cursor distance, but with this new modset, it has become really shortened.

How do you adjust the cursor reach / detect object distance? I've tried searching google, the fallout wiki and these forums, but couldn't find an answer.

I didn't know it could even be changed? Try going into sneak mode. You will be closer to the ground, so you should be able to reach them easier. Also if your Explosives skill is really low, you have to be super quick to disarm them.

Probably the gamesetting fActivatePickLength? I'd just filter the gamesettings by 'Activate' and see what there is.

That's right, although it's an integer in Fallout 3 - "iActivatePickLength". The default is 150, if I remember correctly

Cipscis

Well to keep things simple, you can get the Groovatron which has a long reach mode. Press the hotkey and you can now disarm those mines from a distance. Press the hotkey again and it's back to normal.

Methinks Mr. Gary is poking fun at your expense.

... Unless the Groovatron is from a mod.

The Groovatron is a mod brudda.