I was doing small boil and late addition (extract) way back in 1994 (years before it was "officially" designated to be "discovered" by a well known brewer)
I was doing so because I had small pots at the time.
To answer your question, since you are doing a full boil then just add it all in.
What I "discovered" (not really) about small boils was really based upon hop utilization. I was worried more about the balance of the brew. Achieving a better color (not too dark) was a bonus.
Way back then I read Papazian's The Complete Joy of Homebrewing (1st ed) nearly every day. I have the 3rd Ed now so I will refer to it.
My "AHA!" moment was when I read the Hop Utilization Chart on page 258. The second block (going downward) reads: "LBS OF MALT EXTRACT PER GALLONS OF BOILING WATER". Then reading across it identifies the 1 lb through 5 lbs.
I thought, since I only boil 2 gallons why not add only 2 lbs of malt and add the rest at the end? This maxes out (or is close enough) the hop utilization at 60 mins.
Anyway, it always worked for me.
I do all grain full boils now and don't do all extract anymore, but it's difficult to lose knowledge...unless you're Gary Busey.