Adjusting scale of bubbles in BubbleChart with python-pptx

Question

I'm looking for help scaling the size of bubbles in a python-pptx bubble chart, so I have managed to plot a bubble chart using python-pptx and using the following data:

Risk	Yield	R-adj	Type
0.10	0.15	0.015	Cash
0.40	0.50	0.025	Money Market
0.60	0.20	0.015	Government
2.20	5.30	0.065	HY Bonds
1.20	2.20	0.050	IG Bonds
1.45	3.50	0.053	Yield-Enhanced
2.20	3.50	0.044	Equity Infra

where 'data' variable below is a pandas.DataFrame object representing the table above

from pptx import Presentation
from pptx.chart.data import CategoryChartData, ChartData, BubbleChartData
from pptx.enum.chart import (XL_CHART_TYPE, XL_LEGEND_POSITION, XL_LABEL_POSITION)
from pptx.util import Inches, Pt

prs = Presentation(r'template.pptx')
slide = prs.slides[0]

# Create bubble chart
chart_data = BubbleChartData()
for i, asset in enumerate(asset_type):
    series = chart_data.add_series(asset)
    x, y, z = x_series[i], y_series[i], z_series[i]
    series.add_data_point(x,y,z*0.5) # changing z value doesn't change the size of the bubbles

# x, y, cx, cy = Inches(10.8), Inches(4.0), Inches(0.4), Inches(2.4)
x, y, cx, cy = Inches(0.5), Inches(2), Inches(10.8), Inches(4.3)
chart = slide.shapes.add_chart(XL_CHART_TYPE.BUBBLE, x, y, cx, cy, chart_data).chart

# Config legend
chart.has_legend = True
chart.legend.position = XL_LEGEND_POSITION.BOTTOM
chart.legend.include_in_layout = False

what I have done is trying to adjust the size of 'z', the size variable, however it seems that changing this value doesn't change the size of the bubbles as it seems that the size of bubbles are proportionate to the plot area, where the largest bubble is x% of the area of the plot, does anybody know how I could adjust the scale of the bubble?

And also include data label on the bubbles, rather than having a legend?

Thanks, any help would be appreciated.