Trem Route Sustain Block Distance?

[Mickguard]

Another trem question I can't seem to find info on...

Is there a rule of thumb for the distance of the gap I'll need to leave between the sustain block and the front edge of the top route?

I'm trying to figure out the exact location for the front edge of that route --I want to be able to set the trem in there so that the High E saddle falls exactly on the intotation line. (I've set the saddle to an optimum position to give me some play forwards and backwards, for all saddles).

On my strat it looks like there's a good 2 mm gap there, but it's hard to say (don't want to take the guitar apart) --at any rate, the trem I'm using has much different dimensions (it's smaller). So I'm not able to work with the template drawing in the Hiscock book. And Stewmac doesn't help because their fret scale calculator pretty much assumes you bought the bridge from them --so they measure to the center of the front screws, which doesn't work for my bridge.

How much of a space do you leave? Is there a way of measuring that based on the pivot edge?