ADC Conversion time doesn't change when changing the sampling time

Hello,

at the moment i try to verify the conversion time of the ADC that is described in the datasheet.

I measure one channel in regular conversion mode without interrupt. 

To calculate the conversion time i used the equation in the datasheet.

Tconversion = tsampletime + ConversionTime

The resolution is fixed with 14bit -> 17 ADC cycles.

ADC clk = 3682540Hz.

I toggle a pin after starting the ADC and i toggle the pin again when EOS flag bit is set: 

GPIOA_NS->BSRR |= GPIO_BSRR_BS0;

while((ADC1->ISR & ADC_ISR_EOC) != (ADC_ISR_EOC))
{
}

GPIOA_NS->BSRR |= GPIO_BSRR_BR0;

I measured the Conversion time with the ocilloscope.

Here are the results ( at the left hand side the measured conversion time and at the right side the calculated):

There is a delay of 6us because of the pin toggling that i have also taken into account for the measurement results!.

My question is: Why stays the conversion time the same for the first 3 sampling time configurations?