Youre not seeing better odds, its just the crosses with the hets have been broken down more.
Spider x normal gives you half spiders and half normals (50/50).
Visually, spider x het clown will also give you half spider and half normal (again, 50/50).
However the genetics calculator is adding in the het. So you get:
25% Normal
25% het Clown
25% Spider
25% Spider het clown
Because 25% + 25% = 50% you are still looking at 50% visual SPIDER (oops).