URGENT :Need an Enquiry

hi guys,
i wanna to ask you about the effect of the air region arround a conductor regardless the software i use
1-why the size of the air arround a conductor affects its inductance value (as i measure its inductance)( parasitic extraction)?
2- to what extend can i get its accurate value if the conductor is uncovered and touch the overall air?
3- my estimation:
i think that maximize the size of the air region may increase the inductance value but slight increase not To some extent large increase as the air Limits more flux but it has a weak effect(with small flux density values) please give me your comment on my estimation i will attach you with the result excell sheet ,the figure of my simple project and the figure of flux density(complexmag_B)