Next buy price PC / ( #S x ( 1 + SAFE + Minimum Trade Size ) ) = 30 / ( 1 x 1.2 ) (assuming 10% safe, 10% min trade size) = £25 next buy price
Next Sell Price PC / ( #S x ( 1 - SAFE - Min Trade size ) ) = 30 / ( 1 x 0.8 ) = $37.50
For much of time the price might be rattling along close to the next sell price (upward price movement), so generally a decline from close to $37.50 (next sell price) down to $25 (next buy price) is around a 33% decline
i.e. most AIM'ers like a initial "third off" sale price, not a lousy 5 cents off a $30 shirt.
After that discount AIM will however buy even more stock after relatively small subsequent discounts (average in more relatively quickly if the price continues on further down).