I haven't bothered modding ships yet, but like Goblin Wizard mentions, ships come in many different variations.

When we say "Bident" we think "oh, missile ship", but when you run a search though the definitions in Carcasses.xml there's actually 8 versions of those. Then from those 8 definitions, ShipDescriptions.xml expands it into 23 actual loadouts -- I'm guessing the player one is the one with the "_pl" tag (the others are like "_pat" for patrol and "_tri" for Triada). I'm not quite sure why they have a number behind them, though (_pl0, _pl1), but it's likely just multiple variations of the same ship for that faction.

This is why I haven't bothered with ships yet. Too many variations to keep track of. I might be using my script to tweak the hp and shield restore values though.

Not just ships but missiles have this EPR value as well. In Rockets.xml, all rocket definitions are using the same EPR value (0.05). I'm not sure how it relates to radar, because in Modules.xml rocket entries don't have a radar range - they simply have min/max firing range. Additionally, detonators for MIRV-type rockets have a <radius_search_target> value. I suppose this is "radar" for the secondary warheads it splits into.

In Modules.xml radars modules have 2 values, resolution and max_distance. In Carcasses.xml ship definitions only have EPR value (just like missiles? hmmm).

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Edit:
One more thing, I was comparing the so-called rapid fire heavy guns and kinetic heavy guns because one of the gunnery perks says it improves skill on both "small guns and rapid fire guns". But looking at the Modules.xml entry for the M-106 Bardiche ("HC1", heavy kinetic gun) and the M-200E Vulcan ("VC1", heavy rapid fire gun), how does the game tell one is a rapid fire weapon while the other is not? They are both using IMPACT damage_type. Actually even plasma guns do IMPACT damage (huh wtf??). So I took a closer look at the guns, and all of them either deal IMPACT or LASER damage. Only two types of damage?

There is a graph_type, and this one does show more variety (BIG, SMALL, PLASMA, LASER) but I thought this was referring to the projectile graphics. By the way it seems like the sfx_index are referring to entries in \Data\PFX\Projectiles.sfx (e.g. the Alien gun "ASG" is type SMALL and sfx index 2, and if you look into Projectiles.sfx under the small guns' entries ("TracerSFX_"), the third entry (0, 1, 2) has a COLOR RGB index of 14,144,215... exactly the light blue colour of the alien gun's bullets.

I need to find the perks so I can see how gunnery is being calculated.