"contribute mostly" is correct and usable in written English.
You can use it when you want to describe something that makes up the majority of a given sum or amount. For example, "The contributions to the fund came mostly from wealthy donors."
All these sweeteners when added to drinks contribute mostly empty calories that do little to satisfy the appetite and end up as excess energy that the body ultimately turns to fat.
We have determined those recurrent geomagnetic activity variations which contribute mostly the current sunspot activity.
Analysis of the Reynolds stress structure behind the windbreak shows that the ejection and sweep events contribute mostly to the stress.
Results show that the circumferential modulus provides a major portion of the flexural energy of the vibrating structure while the longitudinal and in-plane shear moduli contribute mostly to the stretching energy.
This positive loading on (text{Ca}^{2 + }, ;text{Mg}^{2 + }) and TH suggest (text{Ca}^{2 + }, ;text{Mg}^{2 + }) that probably contribute mostly to hardness of water in the study area.
The extensive analysis of PAH reaction steps showed that the main reaction routes can be conditionally divided into "low temperature" reaction routes, dominating at T < 1550 K and "high temperature" reaction routes, which contribute mostly to PAH formation at T > 1550 K.
In his first two years of high school, he contributed mostly as a cornerback and a special teams player.
Until Friday, though, Robinson had sat plunked near the end of the bench and contributed mostly by encouraging.
He has played in 77 games over all, starting six and scoring two touchdowns, while contributing mostly on special teams.
This imprecision is supposed to be contributing mostly to the inconsistencies between observations and computed predictions.
The analysis revealed differential in-plane translations and rotations between floors contributed mostly to gravity load.
