If exposure is correct, that gives you a base. Make one or more contacts changing exposure if you must.
Make your contact print at 8x height and and 8x10 will print at the same time/aperture. With 35 mm. 3.5x 5x 8x 11x and 16x progressively reguire double the time plus resciprocity compensation if you alter time.
Test strip is a narrow strip that spans highlight & shadow. A whole sheet is very expensive and you gain nothing. It does not matter the angle of the strip, just get it to cover the right places.
Lay a strip of cardboard down so you place it properly.
Trust me, sloppy exposures are expensive also. My contact sheets are all uniformly exposed. Saves a ton of time and expense.