What dictates what gets shot at first in a fleet battle?

I'm trying to discern whether it's better to have a mixed fleet, or what.

Are tiny ships worth taking (not counting starbase influence) in conjunction with Small, Medium, and Large hulls? The way I have done fleets is to make 2 or 3 medium ships, 1 large ship, and 4 to 6 small ships.

In the specific game I'm playing, at Painful difficulty, I'm in the phase of research where Large is as high as I go. Enemy defenses are negligible, and he uses beam, so I've outfitted Beam defense on my Medium and Large Ships (he attacks with 14, I have 10 defense on these) and 4 on my tiny ships. My attack rates are about 9 beam on Tiny, 12 on Medium, and about 12-15 on large (my larges pack 20 defense, sensors, and are faster than other ship classes for versatility and getting around).

I'm certainly winning the fleet battles, but am I being inefficient with the use of Tiny ships. Would it be better to use small/medium exclusively? I obviously have a difficult time keeping 6 to 8 HP ships alive.

How can I improve my ship loss ratio?