Brake line size question

Hey all. Long time since posting and now getting back into my CJ5 and commando.
Reworking the brakes with new MC and proportioning valve and due to different size ports, I'm questioning if the tubing size matters.
Such as one line off the MC needs to reduce from 5/16" - 1/4", and the rear line from 1/4" - 3/16". Does it matter if I run large and reduce vs. reducing and running small.
I know there was a front lockup issue with the trucks and wagons that was solved by changing one line up one size.

 

All the line should be the same (3/16")....the fittings are different sizes. Brake fittings are measured differently, my M/C has 1/2" fittings. The proportioning valve has 7/16" fittings for the rear, and all the rest are 3/8". If any of you guys can add please do....

 

I think you pretty much nailed it...I have always used 3/16 front to rear..the line is probably the same size on yours just the od of the fittings is larger which is common.