Issues, Workarounds & Localization

Hello everyone, I'm a noob so my apologies if this has already been discussed elsewhere.
I've recently started the Eve adventure on my laptop which, while no beast, has been able to handle older games just fine (Dishonored, Warframe, Assassin's Creed 3...). Now with everything on high settings, save for AA and shadows, when moderately zoomed in, I get an average of 40-50 fps with peaks at 60, which is good enough to play. However deepspace mission encounters are often very laggy, I drop to 30 and even lower if there is gas in the area.
Flying around the big stations with their many little details won't affect the framerate, neither will the warp and its insanely beautiful particle effects, or lasers and explosions (the big battle at the end of the Minmatar tutorial went smooth) but some ugly asteroids and vague gas clouds will tear my fps apart.
Why is that ? Obviously it's an optimization issue of some kind but I wanna now if it is on my side or on the game's side.

Anyone can comment on that ? Thanks !