Shimano STI shifters: do they come in different sizes?
Yes.
Shimano introduced the 3300 STI in 1999, which has a downshift lever on the hoods, and reach adjust via screw (the main models had only rubber shims to adjust reach). This continues today as Tourney ST-A070. Generally people are quite rude about this as it is 'not pro' but it will suit some people better.

The third release of Dura-Ace brifters was 7800, and these reduced the grip circumference by 5mm compared to earlier releases, to fit smaller hands, as such products tend to be designed for average-sized men, not women or men with small hands.
7800:

vs 7700:

R700 was then a specific 'small hands' short reach model

The introduction of a hydraulic master cylinder complicated the design. The first one was Di2, which meant no mechanicals and buttons for shifting so these weren't too huge

Shimano has a habit of making clunky shifters for the low-end, and because they were charging exorbitant premiums for hydraulic brifters, came out with ST-RS405 as a cheaper version, which caused many complaints because of its bulbous shape

The pointless (and now cancelled) 'urban' groupset Metrea also experimented by moving the bleed port around which resulted in this monstrosity

Eventually Shimano settled on a hydraulic design which was not too ugly and which is now basically standardised across the range (small differences for gravel, and a bit smaller for Di2):

The one above is ST-R7020, there is also ST-R7025

which is the same but with 4mm less reach, for smaller hands (these brifters all now have screw adjustment as well). Similar models are R8020 vs R8025, and 4720 vs 4725
So several different current sizes:

Di2 (because no mechanical shifting) + cable brakes
Di2 + hydraulic brake
Tourney A070 hood shift type
Mechanical hydraulic brakes (plus various discontinued versions)
Closer reach version of the above
Mechanical cable brakes (plus various discontinued versions)
GRX Di2 hydraulic (higher hood because 'gravel')
GRX mechanical hydraulic