RC - connection using RCTime produces strange results

Dear readers,
I have attached a RC connection to a Microchip's pin.
Pin ---- 0 to 40 kOhms ---- 100 nF ---- GND

1. Make Pin high
2. Let wait for 20 ms
3. Set pin to high-impedance
4. I let wait, till pin Low becomes low - counting while doing so

Depending on R value it is faster/lasts longer to make pin Low.
I make the value of R be constant and do several measurements. The result is visualized for me.

What can I infer from these values ?

Code:

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W1:
        ADCWert = 0                  ;I         
    TRISA.3 = 0
    PORTA.3 = 1
    Pause 3
   
    ;PORTA.3 = 0                  ;II
    TRISA.3 = 1
    WHILE PORTA.3 = 1
        ADCWert = ADCWert + 1
    WEND     
   
    TRISA.3 = 0                  ;III
    PORTA.3 = 0
    Pause 18

W2:
    ADCWert = 0
    Low PORTA.3 ; Discharge cap to start
    Pause 10 ; Discharge for 10ms
    RCTIME PORTA.3,0,ADCWert ; Read potentiometer on Pin3
       
W3:
        ADCWert = 0                  ;I
    TRISA.3 = 0
    PORTA.3 = 1
    Pause 3
   
    ;PORTA.3 = 0                  ;II
    TRISA.3 = 1
    WHILE PORTA.3 = 1
        ADCWert = ADCWert + 1
        TRISA.3 = 0
        PORTA.3 = 0
        TRISA.3 = 1
    WEND     
   
    TRISA.3 = 0                  ;III
    PORTA.3 = 0
    Pause 18   
 W4:
        ADCWert = 0                  ;I
    TRISA.3 = 0
    PORTA.3 = 1
    Pause 3
   
    ;PORTA.3 = 0                  ;II
    TRISA.3 = 1
    RCTIME PORTA.3,1,ADCWert   
   
    TRISA.3 = 0                  ;III
    PORTA.3 = 0
    Pause 18

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