Hmm, interesting. According to the LoF rules: Unless otherwise indicated for specific purposes, Markers do not obstruct LoF. Nothing in the Motorcycle rules override this so I guess the Motorcycle marker doesn't block LoF.
The rider needs to be in b2b with the silhouette to mount it. The Silhouette matters for enemies wanting to attack and destroy the unattended bike. Troopers cannot move through non-friendly silhouettes.
I don't see what there is to house rule. The rules are VERY clear. A player activates their motorcycle trooper and declares dismount. Per the rules they can place a motorcycle marker or scenery with similar diameter. The rules on scenery are VERY clear. The rules for markers are VERY clear. The precedent of how markers vs scenery works has been set by objectives. The situation is also intuitive and non-gamey as well. Bottom line is that if you don't have a spare unmounted bike scenery piece you get no cover. Honestly, I suspect the only confusion likely stems from cognitive dissonance where people assumed they knew how motorcycles worked and their brain is jumping sideways, because I really don't see where the actual grey area is in the actual evidence. (Penny's dismounted version used to lack impetuous in the army builder for awhile. So for awhile she could hop off her bike and use it for cover.)
Funny enough I bought the model. If only to have something to use as an Aragoto for now since it seems to fit for now. :P
Reminded me of my old conversion made before the bounty hunter bike release. Never played her though.
I sculpted a milestone with greenstuff and used her on a 25mm base. I am afraid a bike and an objective marker are not the same to grant cover hence the houserule part.
Have her doing a wheelie on a 25mm base, sorted. She can join the Umbra Samaritan with completely reasonable Silhouette 2 models.
Maybe look into dire foes 5? The hazmat HVT is almost the same outfit as the biker and limited sniper ABH. I think wrist and shoulderpad are different. And much easier to get than the sniper ABH @.@