I too use the Paterson tanks and use the amount stipulated on the base. Never had a problem with too little developer. I do have problems sometimes loading 120s - usually after an awful long time *not* shooting and processing. 
If it gets really bad, I feed the end that had the tape on it (tear off the part that adheres to the backing paper) and the extra thickness usually gets me out of trouble.
-Nanette

If it gets really bad, I feed the end that had the tape on it (tear off the part that adheres to the backing paper) and the extra thickness usually gets me out of trouble.
-Nanette
