Control the hi-hat before changing the whole groove
Separate the length of the hi-hat sound from how hard you strike it.
If the cymbals are covering the rest of your groove, listen to the hi-hat by itself first. Opening it lets the sound ring longer; striking harder changes the attack and volume. Trying both changes at once makes it difficult to hear which one the song needs.
Hear what the foot changes
Count "1 & 2 & 3 & 4 &" and play eight evenly spaced hi-hat notes with the cymbals closed. Choose a comfortable practice tempo. Repeat the bar with the same hand motion, but ease the pedal up for the hit on beat 4 and close the cymbals on the next 1.
Listen for a longer note on 4 and a clean return to the closed sound. If the opening shifts your timing, repeat just "3 & 4 & 1" slowly until the foot can move without disturbing the hand. The cymbal gap should allow the sound you want, rather than match a fixed measurement.
Hear what the hand changes
With the pedal closed again, play a bar of quiet eighth notes, followed by a bar with a stronger note on each numbered beat. Keep the & notes quiet. This is an accent exercise, not a part every song needs.
Compare the recordings. You should hear the accent pattern without extra notes or uneven spacing. Also compare the tip and shoulder of the stick at a similar playing effort; your cymbals may respond very differently, so choose the sound by listening rather than by a promised volume change.
Put it back in the groove
Add kick on 1 and 3 and snare on 2 and 4 for a simple 4/4 practice groove. Try the closed version, then the single opening. If the kick arrives late after the opening, return to the foot exercise. At rehearsal, ask whether the longer cymbal sound helps the transition or covers the vocal.