Slider Indicator is not over the thumb initially

It is a custom Slider I made but on screen starting the indicator is on corner not above thumb. I don't know what's the reason

Here's my paint code for thumbshape

void paint(
    PaintingContext context,
    Offset center, {
    required Animation<double> activationAnimation,
    required Animation<double> enableAnimation,
    required bool isDiscrete,
    required TextPainter labelPainter,
    required RenderBox parentBox,
    required SliderThemeData sliderTheme,
    required TextDirection textDirection,
    required double value,
    required double textScaleFactor,
    required Size sizeWithOverflow,
  }) {
    _indicatorShape.paint(context, center,
        activationAnimation: const AlwaysStoppedAnimation(1),
        enableAnimation: enableAnimation,
        labelPainter: labelPainter,
        parentBox: parentBox,
        sliderTheme: sliderTheme,
        value: value,
        textScaleFactor: 0.6,
        sizeWithOverflow: sizeWithOverflow,
        textDirection: textDirection,
        isDiscrete: isDiscrete);

    assert(sliderTheme.disabledThumbColor != null);
    assert(sliderTheme.thumbColor != null);
    assert(!sizeWithOverflow.isEmpty);

Can you suggest why it is happening?

For reference:-