raycasting problem

[lilac kraken]

i want to raycast onto a meshpart but the raycast also detects the empty parts which isnt what i want i want the raycast to be projected on to the geometry of the part how can i do it like that

[dusk fog]

Shapecasting

[lilac kraken]

thats not what i mean

when i raycast onto this

it also detects the empty parts

it rays onto the whole selection box