cross angle means to direct the tweeter to face the center...usually to face the tweeters to the rear-view mirror or center of the car for sound staging purposes...

err.... not sure what is crossed angle but one thing i'm pretty sure, don't put the tweeters direction facing to u, (given if u had the crossover installed with the tweeters) or u end up suffer the direct high frequency sound produced by it x_x

I did it before right after i installed my ICE and end up can't  turn the volume loud coz the tweeter was 'shooting' my ears badly
or maybe becoz my components set was cheap after all?

i think this topic is very subjective to the types of tweeter that you are using...

pass experience,

metal dome tweeters: i place them high up on the a-pillar somewhere till my ear level while the left tweeter faced my left ear and the right side faced the passenger's right ear... result was good... harshness was minimized while the staging was high enough...

then i change to soft dome: using the same angle... i found that my staging is too close to me... even how i cut the freq, adjust the gain... still they are too close... then i place then deep into the dashboard on the a-pillar faced where still the angled like before towards the ear thing and upwards to the rear view mirror... results well staging not so high... but its very deep...

of all these two setup... my cross point had no real changes... only minimal changes that unless you have a diamond ear... then you will notice them...

so what tweeter are you using?