Platinum Preppy EF pen stroke

My fountain pen Pilot EF nib is in ink flowing trouble, so I bought new one Platinum Preppy EF, but failed. The Preppy nib does not offer extra-fine lines. Ink flowing too much and the relation between the pen pressure and the line width is disturbed.                                        

not thin lines

line width not stable

 Lines, especially thin lines cannot be stably drawn.
 800yen in the fountain pen and the converter. Pilot EF is better.

Platinum Preppy 02