It is bad :)
I is a special letter in Polish:
The letter "I" can inform about the SOFTNESS of preceding consonant (C, DZ, N, S, Z) and mark the SOUND [ I ] (e.g.) - it is before consonant
siła (r: śiła) not as "s-iła" or "śła"
wozić (r: woźić) not as "wo-z-ić" or "woźć"
The letter "I" can inform about the SOFTNESS of preceding consonant (P, B, G, K, W, F, CH, M, N, L) and mark the SOUND [ J ] - it is before vowel -- there is a different arrangement of the tongue with the pronunciation of softened sounds [ '] (with an additional movement of the tongue towards the hard palate) than with hard ones [without] (e.g.)
radio (r: radjo) as rad'jo but: radość
wiara (r: wjara) as w'jara but: wara
piasek (r: pjasek) as p'jasek but: pasek
The letter "I" can be only a graphical sign of SOFTNESS of the preceding consonant (but it does not mean a separate sound) - it is in fact the equivalent of a diacritic mark (a line that appears in the letters: ć, dź, ś, ź, ń) - it is before vowel (e.g.)
zioła (r: źoła)
w wodzie (r: w-wodźe)
The letter "I" can be only the SOUND [ I ] - when the letter appears after a vowel or a pause - it is before consonant (e.g)
I suppose that quite a lot of non-Polish people don't even realize the difference between ć/ci and cz, which makes it difficult for them to pronounce it correctly. It may be helpful to insert a slight j, like 'ćjasto', to get close to it.
It's the same thing with ś/si and sz, also ź/zi and ż.