I have the same question as the OP, but unfortunatley the "best answer" that was given was with reference to the Small Harbor for Taxpayers which is an altogether different provision. That safe harbor is concerned with the total of all expenses, not individual expense items.
As per the OP, I'm interested specifically in how to apply the $2500 De Minimis Safe Harbor (not the Small Tax Payer, nor the Routine Maintenance Safe Harbors) when there is partial ownership and thus a corresponding percentage share of the expense.
The dollar limit under the De Minimis provision is stated to apply "per invoice" or "per item as substantiated by the invoice". I'm not certain if this implies that the original invoice amount cannot exceed $2500 period (i.e. so if you own 50% then tough luck, you only get $1250 for the safe harbor), or whether that can be interpreted in relation to your share of the invoice (i.e. original invoice could have been $5000, but as your share would be $2500 you are fine to apply the safe harbor).
Thank you
