you probably would need 400mm or even 500mm pots to do what you want to do, but from what i know of the mock orange their root system is very large and very many, we removed 4 from a garden here they where about 1 meter high it took a bob cat to do it. swore i'd never grow them again they are drought hardy but take all moisture from the soil making it hard for other plants.
surely they can't be too expensive to buy?
With peace and brightest of blessings,
"Be Content With What You Have And
May You Find Serenity and Tranquillity In
A World That You May Not Understand."