What I interoperate the OP as asking is this.
he is saying: "I used this additive & it seemed to him that it helped".
Then he is trying to apply & Use the logic that:
---------------" if some is good, then more is better
Let me tell you that the resounding answer is: " NO !!".
Additives do not replace oil & are not better than your base oil for lubrication of the internal moving parts of you diesel engine.
They are meant to be used in relatively small quantiles & not to replace 20% of your lubricating oil.
OK - if you want - So you could go to 40 wt. oil & that would be OK as long as your going to use a top quality DIESEL rated oil.
If you insist on using an additive, Use the quantity of Lucas oil treatment you say you used the first time. -- That will probably be OK - maybe.
BUT DO NOT REPLACE 20% of your oil capacity with additive.
Nuff said !