I'm no expert but like you have read a fair bit on the subject and it makes logical sense to me that regardless of the scale length, if you capo the first fret and fret wherever the neck meets the body then measure the middle fret. This assumes string height at the nut and around the twelfth fret is close to manufacturers recommendations. I'm happy with around .006"-.008" clearance measured with engineering feeler gauges. I've read to use a business card but they can vary tremendously. If you have little or no clearance and a high action then I would suggest bridge adjustment is required to get the action right first, then tweak the truss rod to get the clearance you need. All this depends entirely on how you play i.e. an aggressive strummer will need more clearance than a light fingerpicker, the holy grail being the lowest action for ease of playing "your style" without a hint of string buzz. Carefully removing material from the bridge base is irreversible but not the end of the world, just buy another bridge if you goof. Truss rod adjustment is dead easy to rectify if you overdo things. There are far more experienced guys on this wonderful forum who may disagree but for me it's about getting it right for yourself rather than focussing on set dimensions. Have a go at it, it's fun to learn.
