大乘百法明門論開宗義決 1.99

1.99

以長短等亦色處收者。夫言處者生識為義。色生眼識故色為處。若使長短眼識不緣則非生識。寧色處收。

Regarding "because long, short, etc. are also subsumed under the form base": "Base" (āyatana) fundamentally has the meaning of generating consciousness. Form generates eye-consciousness, so form is a base. If eye-consciousness did not take long, short, etc. as objects, then they would not generate consciousness; how then could they be subsumed under the form base?